Electrical circuit arrangement



p 24, 1946- H. D. GARRETSON 2,403,017

ELECTRICAL CIRCUIT ARRANGEMENT Filed May 5. 1943 HARRY D. GARRETSON INVENTOR.

ATTORNEK. i I

Patented Sept. 24, 1946 UNITED STATES PATENT OFFICE ELECTRICAL CIRCUIT ARRANGEMENT Harry Douglas Garretson, Whitestone, N. Y., as-

signor to Philips Metalix Corporation, New

York, N. Y.

Application May 5,

Claims.

justable by a sliding member adapted to move over bared turns of a transformer winding. The invention is especially applicable to adjustablevoltage auto-transformers having a step-down ratio and will be described in this connection.

Transformers of the above specific type usually comprise an electrical winding having a fixed voltage portion and an adjustable voltage por tion. In practice, the two portions of the winding are spatially separated in order to provide proper access of the adjusting slider and its operating mechanism to the adjustable-voltage per tion of the winding. In the case of transformers comprising a rectangular magnetic core, the fixed voltage and the adjustable portions of the transformer Winding are each Wound on a separate leg of the magnetic core.

While this construction simplifies the mechanical design of the transformer, I have found that it introduces certain electrical disadvantages, more particularly, this construction produces a transformer having a high leakage reactance and characterized by poor voltage regulation.

It is an object of the invention to obviate the above electrical disadvantages.

A more specific object of the invention is to provide novel circuit arrangements for transformers of the above described type by which the effective leakage reactance of the transformer is reduced without sacrificing the mechanical advantages of the transformer construction.

A further object of the invention is to provide simple and economical expedients for improving the voltage regulation of adjustable voltage transformers.

These and further objects of the invention will appear as the specification progresses.

In accordance with the invention, I effectively reduce the high leakage reactance between the fixed-voltage and the adjustable voltage portions of the windings by means of a tertiary Winding which is closely coupled to the fixed-voltage portion and which is electrically connected in shunt with the adjustable-voltage portion.

The invention will be described in greater detail with reference to the appended drawing in which Figure 1 illustrates the circuit arrangement of the invention as applied to an adjustable voltage auto-transformer having a step-down ratio between the input and output terminals,

1943, Serial No. 485,769

Fig. 2 illustrates the circuit arrangement of the invention as applied to an adjustable voltage transformer in which the input and output windings are electrically insulated from each other.

Referring to the drawing, the transformer of Fig. 1 comprises a rectangular magnetic core It on two legs H and I2 of which are two windings l3 and M respectively, connected in series additive relationship to input terminals !5 and [6. A continuously adjustable voltage is obtained at output terminals 13 and I9 from the winding [4 by means of a slider I! which contacts bared portions of the winding I4. The voltage appearing at terminals 18 and 19 has a Value determined by the position of the slider I! relative to the interconnection between windings l3 and M to which the terminal 19 is connected.

As above pointed out, the leakage rectance normally existing between windings l3 nd [4 causes the transformer to exhibit poor voltage regulation. In accordance with the invention, the leakage reactance of the transformer is effectively reduced by means of a tertiary widing 20 which is connected in shunt with the Winding I4. Winding 20 is 50 coupled to winding l3 that substantially all of the magnetic lines induced in the transformer leg H by the winding [3 are linked with the winding 20, Such a close coupling is obtained by superimposing the winding 20 over the Winding I3.

The number of turns of the winding 20 is so determined that under no-load conditions the voltage induced in the winding is equal to the voltage appearing across the winding M.

In usual practice, the transformer of Fig. 1 has a step-down ratio of 2 to 1, i. e. the maximum voltage obtainable across the terminals l8 and I9 is equal to one-half the voltage applied to terminals l5 and I6. In such a case, the windings l3 and H! are symmetrical and to obtain the improvement in regulation in accordance with the invention a Winding 20 is used having the same number of turns as the windings I3 and [4.

The transformer illustrated in Fig. 2 comprises a rectangular magnetic core 30 having a winding 3| positioned about a leg 32 of the core and connected to input terminals 35 and 36. P0- sitioned about a leg 34 of the core is an output winding 33 one end of which is connected to output terminals 31. The output voltage of the transformer is adjustable by means of an adjustable slider 39 adapted to contact bared portions of the winding 33 and connected to a terminal 38. Windings 3| and 33 are electrically insulated and their turns ratio may be step-up or a step-down as desired depending on the requirements to be met by the transformer.

In accordance with the invention, the leakage reactance existing between the windings 3| and 33 is elfectively reduced by means of a tertiary winding dil which is connected in shunt with the winding Winding Mi is superimposed on the winding 3! and so coupled to it that substantially all of the magnetic lines of force induced in leg 32 are linked with the winding 43. The number of turns of winding 40 is so determined that the voltage induced in thi winding is the same as the voltage induced in winding 33.

It should be well understood that while the invention has been described in connection with transformers having a continuously adjustable voltage output, the invention is equally applicable to transformers in which the output voltage is adjustable by means of a plurality of taps of the output winding.

While I have described my invention by means of specific examples and in specific embodiments, I do not wish to be limited thereto for obvious modifications will occur to those skilled in the art without departing from the spirit and scope of the invention.

What I claim is:

1. An electrical transformer comprising a magnetic core, two magnetically coupled windings on said core and so positioned with respect to each other that a substantial amount of leakage reactance mists between. the windings, and a tertiary wins. on said core tightly coupled magnetically to one of said two windings and connected in shunt with the other of said two windings.

2. An electrical transformer comprising a magnetic core, a winding on a portion of said core, a second winding on another portion of said core, and a tertiary winding on said core superimposed on said first winding and connected in shunt with said second winding.

3. An adjustable voltage transformer comprising a magnetic core, a winding on a portion of said core, a second winding on another portion of said core, and so positioned with respect to said first winding that a substantial amount of leakage reactance exists between the windings, a slider member adapted to contact bared portions of said second winding, and means to reduce the effective leakage reactance between said windings, said means comprising a tertiary winding on said core tightly coupled magnetically to said first winding and connected in shunt with said second winding.

4. An adjustable voltage transformer comprising a rectangular magnetic core, a winding on said core having a portion positioned about one leg of the core and a second portion positioned about another leg of said core and interconnected in series relationship with said first portion, a slider member adapted to contact bared portions of said second winding for providing an adjustable voltage proportional to the part of said second winding portion between the slider contact and the interconnection between the winding portions, and a winding on said core superimposed on said first winding portion, connected in shunt with said second winding portion and having an induced voltage equal to the induced voltage of said second winding portion.

5. An adjustable voltage transformer comprising a rectangular magnetic core, a winding on a leg of said core, a second winding positioned on a second leg of said core, electrically insulated from said first winding and so positioned with respect thereto that a substantial amount of leak age reactance exists between the windings, a tertiary winding on said core superimposed on said first winding and connected in shunt with said second winding, said third winding having an induced voltage equal to the induced voltage of said second winding, and means for contacting selected portions of said second winding for providing an adjustable voltage proportional to the portion of the winding interposed between said means and the end of the winding HARRY DOUGLAS GARRETSON. 

